In adaptive array circuits, a need exists for a correlator (multiplier) with specific properties. One of the properties is essentially zero DC output whenever either of two inputs is zero or whenever the inputs are in phase quadrature. It is especially important that a zero output be obtained, when appropriate, over large dynamic ranges of either input. Another property is that one or both of the input signals be very weak even at the peak of dynamic signal variation. Under these conditions a useful high level correlation signal is desired. Very strict adherence to a perfect multiplication law is of secondary importance.
In a straightforward low offset design (referred to as "a low offset correlator design"), the basic correlator design met all of the above objectives, DC offset errors and l/f noise in operational amplifiers following the correlator overshadowed the basic correlator performance given weak signal inputs. These effects reduced the potential usefulness of the design. In the correlator of the present invention, the DC and l/f noise problems are alleviated, resulting in a much more sensitive and versatile design. The design allows low noise AC amplification of the correlation signals which are then synchronously demodulated at high level.